Severe Weather Threat Saturday Afternoon/Evening

We continue to be in a very active weather pattern, which will continue through Sunday before we get a break.

Today, a weak disturbance will come east, I don’t expect much, but isolated to scattered showers and storms will be possible, any storm that may form as the potential to be strong to severe as colder air aloft interacts with a very warm and humid tropical air mass. Avery warm September day is on tap with highs in the upper 70s interior to upper 80s in urban areas with high humidity, tonight any showers or storms should dissipate but it will be a warm and muggy night as the flow turns SSW ahead of the next and much stronger cold front, lows in the mid 60s to lower 70s expected with high humidity

Tomorrow will be the real day to watch, we see a line of showers and storms over the Midwest, this is associated with a VERY STRONG cold front, there is a strong Canadian air mass behind this cold front , and plenty of clod air aloft with it, tis will again interact with a warm, humid tropical air mass over our area, enhance lifting and cause potential severe weather tomorrow evening. The timing isn’t great for the forecast area so I am not thinking a widespread severe weather outbreak is likely , but I expect a line of showers and storms to come through tomorrow evening, a squall line may develop along the eastern side of this line ad come east, which is something I will watch for tomorrow, and if not, some strong to severe storms will be embedded in this line still.

With the tropical air mass in place ,precipitable water values (PWATS), or in other words, (moisture that can be used for rainfall) will be at 2 inches, or 200% of the normal level, so heavy downpours will be a threat and a likely scene tomorrow, highs on Saturday are expected to be in the mid 70s to mid 80s with very high humidity and a mix of clouds and sun

SPC Discusson:

“ERN PORTIONS OF OH VALLEY…MID ATLANTIC THROUGH NERN STATES… A PRE-FRONTAL SQUALL LINE WILL LIKELY BE IN PROGRESS SATURDAY MORNING FROM THE OH VALLEY SWWD INTO THE TN VALLEY. RICH GULF MOISTURE /UPPER 60S TO 70F DEWPOINTS/ NOW RESIDING OVER THE MID ATLANTIC AND SRN PORTIONS OF NERN STATES WILL ADVECT THROUGH REMAINDER OF THE WARM SECTOR SATURDAY AS SLY LLJ STRENGTHENS IN ASSOCIATION WITH EJECTING SHORTWAVE TROUGH AND DEEPENING SFC LOW. WEAK MID LEVEL LAPSE RATES AND AREAS OF CLOUDS WILL MITIGATE INSTABILITY SOMEWHAT. HOWEVER…BREAKS IN CLOUDS SHOULD ALLOW FOR SOME DIABATIC WARMING OF THE MOIST BOUNDARY LAYER…CONTRIBUTING TO MLCAPE FROM 500-1000 J/KG. STORMS ARE EXPECTED TO INTENSIFY ALONG AND AHEAD OF PRE-EXISTING PROGRESSIVE OUTFLOW BOUNDARY AS WARM SECTOR DESTABILIZES. DEEP LAYER WINDS WILL INCREASE IN ASSOCIATION WITH THE SHORTWAVE TROUGH AND ITS ATTENDANT SFC LOW WITH LARGE HODOGRAPHS AND 40+ KT 0-6 KM SHEAR. ORGANIZED STORMS INCLUDING LEWP/BOWING STRUCTURES AND EMBEDDED SUPERCELLS WILL BE POSSIBLE AS ACTIVITY DEVELOPS EWD. DAMAGING WIND AND MAYBE A FEW TORNADOES WILL BE THE PRIMARY THREATS. VERTICAL SHEAR PROFILES SHOULD BE WEAKER WITH SWD EXTENT INTO NC SUGGESTING DOMINANT MULTICELL MODES. HOWEVER…INSTABILITY WILL PROBABLY BE GREATER IN THIS AREA…AND THESE STORMS MAY BECOME CAPABLE OF PRODUCING ISOLATED DAMAGING WIND AS THE BOUNDARY LAYER DESTABILIZES DURING THE AFTERNOON. “

Areas in red are the most likely to see severe weather, I personally think that should be shifted west and more coastal areas like NYC should be more in the yellow just based on the fact that timing will be at night-time and instability should be falling off but regardless, severe weather will be possible for the whole area, with the main threats being strong winds wich could reach or exceed 60 mph, very heavy rainfall, dangerous lightning and hail.

Once this cold front comes thorough, a much cooler, drier and fall like air mass will drop in from Sunday through next week with highs in the lower to mid 60s over NE PA, mid to upper 60s over NW NJ and East PA and lower to mid 70s elsewhere with lows in the mid to upper 40s NE PA and NW NJ , in the lower 50s East PA and interior NJ and mid 50s along coastal areas, which is slightly below average for this time of year